Inflatable bladders provided on the downstream side of a pivoted panel are known as a preferred approach to providing a crest gate at a dam spillway to control the height of the water behind the crest gate. U.S. Pat. No. 4,780,024 issued to the inventor herein Oct. 25, 1988 and illustrates one form of such a crest gate construction, the bladder being inflatable from a source of pressure to maintain a predetermined water level behind the dam.